Pulsed detonation engines (PDE's) are non-steady combustion devices that typically produce intermittent high-momentum jets of exhaust separated by longer periods of dribbling or no outflow. Such temporal unsteadiness can pose difficulties in many applications. In addition, reliable detonation in such engines requires the use of highly energetic near-stoichiometric mixtures. The use of such mixtures creates combustion product temperatures and detonation-induced velocities that are excessive for most applications. As a result there are several distinct problems that must be addressed in the design of pulsed detonation engines. The severity of each problem depends on the particular PDE configuration, combustion method, and application, and in particular, on whether the output flow is used directly for jet propulsion or is used to drive a turbine.
A first such problem is that the outflow peak temperature, mass-average temperature, peak velocity, and mass-average velocity are too high for many practical applications. Excessive velocity and temperature in the outflow create low propulsive efficiency, limited thrust, and limited device lifetime.
In a gas generator PDE device designed to power a turbine, it is undesirable to have a non-steady or non-uniform velocity turbine flow. Also, gas must be diluted to an acceptable turbine temperature. In a thrust device, a non-steady or non-uniform jet or a high velocity jet has lower propulsive efficiency than a steady uniform jet or a lower velocity jet with the same total kinetic energy. In addition, high velocity jets also produce excessive noise, and high temperature jet engines may be vulnerable to thermal-signature tracking missiles.
Pulsed detonation engine configurations have been proposed to address the unsteadiness problem by using multiple detonation tubes that breathe and fire sequentially and provide a combined inflow and outflow that is temporally more steady than for a single tube. However, these configurations often have limitations that include: the need for dedicated feed and ignition hardware for each tube; flow stagnation in multiple feed distribution exhaust collection ducts; the need for multiple high-repetition detonation initiation devices; the need for complex fast-cycling valving for purging gas, fuel, and oxidant/enrichment; and the need for many pulsing or moving components as well as many parts outside the flow path with significant weight and volume. In addition, stationary tube PDE's have further limitations that include reduced durability based on the need for valves and bearings that transmit thrust. In addition, the noise created by the cyclically loaded parts can pose further problems.
Since pulsed detonation engines have application in important areas such as aircraft and missile propulsion, it is highly desirable to provide a PDE that produces an outflow having velocity, temperature, and outflow characteristics that are compatible with downstream components. In addition, it is desirable to provide such compatibility while minimizing engine losses.